Moisture detection and estimation with multiple frequencies

Abstract

A method of moisture detection and estimation in an absorbent article with use of multiple frequencies is provide that comprises: applying, by capacitive coupling, drive signal of multiple frequencies to a drive electrode in the absorbent article; sensing, by capacitive coupling, sense signal of the multiple frequencies from a sense electrode in the absorbent article; detecting the first wetness event in the absorbent article with use of sense signal of a frequency of the multiple frequencies; and detecting the saturation of the absorbent article with use of sense signal of another frequency of the multiple frequencies.

The invention claimed is: 
     
         1 . A method of moisture detection and estimation in an absorbent article with use of multiple frequencies, comprising:
 applying, by capacitive coupling, drive signal of multiple frequencies to a drive electrode in the absorbent article;   sensing, by capacitive coupling, sense signal of the multiple frequencies from a sense electrode in the absorbent article;   detecting the first wetness event in the absorbent article with use of sense signal of a frequency of the multiple frequencies; and   detecting the saturation of the absorbent article with use of sense signal of another frequency of the multiple frequencies.   
     
     
         2 . The method according to  claim 1 , wherein the detecting the first wetness event comprises:
 detecting the first wetness event in the absorbent article when a sharp jump in amplitude is determined in the sense signal of the frequency that changes beyond a threshold height within a period shorter than a threshold period.   
     
     
         3 . The method according to  claim 1 , wherein the detecting the first wetness event comprises:
 detecting the first wetness event in the absorbent article when a gradual upslope in amplitude is determined in the sense signal of the frequency that changes beyond a threshold height.   
     
     
         4 . The method according to  claim 1 , wherein the detecting the saturation comprises:
 determining in the sense signal of the other frequency a difference in amplitude from the first wetness event; and   detecting the saturation when the difference in amplitude is greater than a threshold amount.   
     
     
         5 . The method according to  claim 4 , wherein the threshold amount is changed depending on the orientation of the absorbent article. 
     
     
         6 . The method according to  claim 1 , wherein the applying drive signal of multiple frequencies comprising:
 applying a periodic drive signal that is swept in a period over the multiple frequencies.   
     
     
         7 . The method according to  claim 1 , wherein the sensing sense signal of the multiple frequencies comprises:
 determining, for each of the multiple frequencies, sense signal by using a bandpass filter.